There are many drawbacks to that cheaper option of wood:
- It’s heavy.
- It can warp in high humidity.
- It’s organic so it’ll degrade over time.
- It’s porous, so you have to be careful of direct contact with water.
- It may require sealing (and resealing).
So, yeah, the material is initially, monetarily cheaper, but you’ll pay for it in other ways.
For instance, if you have to get hurricane protection for your house windows, you could DIY on the cheap with removable sheets of plywood or spend the extra money on true aluminum panels. There is no way in hell I would even consider the wood solution for the reasons I listed above.